This animation shows the warm up of a cold deepwater flowline by the production of warm fluids from the wells at three manifolds at different locations along the flowline.

In this start-up procedure the three manifolds are started in the order of nearest to the production facility (right hand side) first, delaying the start of subsequent manifolds by half an hour.  The top plot is that of fluid temperature along the flowline and riser, initially at ambient temperature, slowly developing to the familiar saw-tooth profile of a daisy-chained flowline system.

This calculation was used to estimate the amount of methanol required to keep reservoir fluids out of the hydrate region.  This was done, using Infochem’s Multiflash hydrate prediction and methanol partitioning algorithms at each position along the flowline at each time.  The amount of methanol required depends on the local temperature, pressure and water flow rate.  Shown in the bottom plot are time traces of the maximum required methanol demand, pressure and arrival (topsides) total liquid flow rate.

Restart surging in the riser (shown in the liquid flow rate plot) increase the flowline pressure to above settle out and steady state pressures for a significant period of time.

Methanol demand has three maxima, corresponding to the start of production from each of the manifolds.  If a well has been shut in for a significant period, the initial fluids it produces are cold and therefore require hydrate inhibition.  As the wells are gradually ramped up the methanol demand increases, until the production fluids start to warm and the demand drops. 

To simplify the operation, it is likely that the real methanol supply would be set at a continuous rate (sufficient to cover the maximum demand), until the system had warmed up.